This invention relates generally to drain or blow down valves for compressed air systems to remove condensed water therefrom, and more particularly concerns an automatic drain valve that at predetermined intervals opens and closes to drain water from a compressed air system.
As ambient air is compressed by a compressor in a compressed air system, the reduced volume of the air causes the water vapor in the air to condense and collect at low-lying points in the compressed air system. If the compressed air system is used to power tools or other delicate equipment, it is necessary that the compressed air be supplied to those tools free of excess condensed moisture. Consequently, it is necessary to remove the condensed water from the low-lying areas in the compressed air system.
The water can be removed from the compressed air system by providing drain valves at the low points in the system which valves can be periodically opened allowing the compressed air to force the water out through the drain valve. Conventionally, such automatic drain or blow down valves are of the rotating ball valve type. The ball valve consists of a spherical chamber positioned between the valve inlet and its outlet. A ball is rotatably mounted in the spherical chamber with a hole drilled through the ball. The ball valve is opened by rotating the ball so that the hole in the ball lines up with the inlet and outlet of the spherical chamber. In order to close the ball valve, a solenoid or motor rotates the ball so that the hole through the ball is at 90 degrees to the direction of the inlet and outlet ports. As the ball in a conventional ball valves rotates toward its closed position, the opening through the ball valve gradually becomes smaller as the hole drilled through the ball engages and is restricted by the edges of the inlet port. As the opening through the ball valve becomes smaller and smaller, the velocity of the water escaping under constant pressure through the restricted opening in the ball valve increases so that substantial erosion of the ball adjacent its hole occurs during the opening and closing of the ball valve. Consequently, such ball valves conventionally have to be replaced every three to six months.
In addition, the water to be drained from a compressed air system may include contaminants which, in addition to speeding the erosion of the ball valve, may also deposit on the outlet port of the drain valve and plug the outlet port. If the outlet port becomes plugged or restricted, it is apparent that the drain valve will not serve its intended purpose. Heretofore, the only way of determining whether a ball valve was working properly was to take it apart for inspection.